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From "Aljoscha Krettek (JIRA)" <j...@apache.org>
Subject [jira] [Created] (FLINK-6383) Add versioning for AbstractStreamOperator state
Date Tue, 25 Apr 2017 16:22:04 GMT
Aljoscha Krettek created FLINK-6383:

             Summary: Add versioning for AbstractStreamOperator state
                 Key: FLINK-6383
                 URL: https://issues.apache.org/jira/browse/FLINK-6383
             Project: Flink
          Issue Type: Improvement
          Components: DataStream API
    Affects Versions: 1.3.0
            Reporter: Aljoscha Krettek
            Assignee: Aljoscha Krettek
            Priority: Blocker
             Fix For: 1.3.0

Right now, {{AbstractStreamOperator}} checkpoints key-group state in {{AbstractStreamOperator.snapshotState(StateSnapshotContext
context)}}. Currently, this is the timers for each key group. We might want to change the
format of this or what we store in the future. In order to facilitate this we should write
a version to the beginning of the stream so that we can deal with schema updates.

For dealing with the fact that we don't currently write a version number we have to at a magic
number add the beginning (think {{0xCAFEBABE}}). For dealing with state that was written prior
to versioning we read the first 8 bytes, buffer them, if they match the magic number we read
the version and from then on jump to the logic based on the version. If the magic number doesn't
match we know we have state from a pre-version version and read the stream using the old code,
including the 8 buffered bytes.

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